Piezo-electric device



P 23, 1931- c. B. SAWYER 7 1,802,783

PIEZO-ELECTRIC DEVICE bri inal Filed Oct. 14, 1927 Patented Apr. 1931 7 UNITED. STATES- PATENT OFFICE CHARLES B. SAWYEB, OF CLEVELAND HEIGHTS, OHIO, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO THE CLEVELAND TRUST COMPANY, OF CLEVELAND, OHIO, A CORPORA- TION OF OHIO rmzonnnoraic DEVICE Application :lled October 14, 1927, Serial No. 226,139. Renewed November 18, 1930.

This invention relates to a new and improved form of piezo-electric sound reproducer and the method for constructing the same.

An object of the invention is to provide a piezo-electric device which will faithfully reproduce impressed electric voltages as sound waves, and which inherently magnifies the mechanical motion of the piezoelectric element without the use of leverages or linkages.

A further object of this invention is to provide an apparatus in which the piezoelectric elements are protected from mechanical shocks.

Another object of this invention is to provide a frame member in which a section of 'piezo-electric material is mounted so that vide a frame member in which the effect of temperature changes of the device is compensated for.

In utilizing the piezo-electric effect of crystals in order to transform electrical energy into sound, it is desirable to have the piezo-electrical material so arranged that comparatively small mechanical movement of the material will cause a relatively large movement of a sound radiating member. One of the best Ways of accomplishing this is to arrange two piezo-electric crystalline portions or sections so that when an actuating electromotive force is applied to the device one crystalline section will expand and the other crystalline section Will contract in a fect of crystalline materials of the Rochelle salt type owing to the fact that their coeflicient of thermal expansion is relatively large and upon a fall in temperature the contraction of the material is greater than the contraction of any metal with which it may be associated. This tends to produce fracture if the crystalline section is rigidly attached, as

crystalline material of the Rochelle salt type is not very strong in tension, and .is somewhat fragile upon the imposition of a sudden shock, although it will stand comparatively large amounts of compression. Metals such as aluminum or magnesium are very advantageous to use in this connection as they have a relatively large thermal expansion, thus minimizing the amount of compensation necessary.

In the drawin s:

Figure 1 is a ront elevation of my device. Fig. 2 is a side elevation with a conical sound radiating member attached.

Fig. 3 is a diagrammatic view showing the movement of the device to which the sound radiating member is attached. 1

The device comprises a frame 1, preferably made of aluminum, magnesium, or similar light metal or light metal alloy. The frame 1 includes an actuating member 2 for a sound radiating element 3 which is shown to be of the conical type. The sound radiatin element is secured to the actuating mem er 2 by means of any suitable securing means, such as a set screw 4, which clamps the actuating pin 5 in the hole 6 of the actuating member 2. The actuating member 2 preferably'includes a thin metal section 7 which gonnects it with the base or supporting memer 8.

The actuating member 2 and the supporting member 8 are provided with abutments or shoulders 9, 10,11 and 12, between which may be mounted portions or secti ns 13 and 14- of piezoelectric material, so that the crystalline sections 13 will engage the shoulside, the section will tend to expand longitudiiially, and when the polarity 1s reversed, it will tend to contract longitudinally. ,Thus, if

. an alternating electromotive forces is applied to the opposite faces of the section, the section will contract and expand longitudinally at a frequency corresponding to that of the ap p iied electromotive force.

e crystalline sections 13 and 14 are also preferably arranged between the shoulders so that when" the inner surfaces are at a potential different from the outer surfaces, one crystalline section expands longitudinally and the other contracts longitudinally, and

this results incausing the actuating member 2 to have a maximum movement substantially transversely to the direction of expansion and contraction of the sections 13 and 14, as shown diagrammatically in Fig. 3.

The support 8 is preferably provided with holes 15 and 16 to facilitate connectingmthe support by any suitable means such as Its 15 and 16' to a block of bee material, such as the block 17 of lead in or er to provide a relatively large mass that will not be responsive to small vibrations, thus insuring that substantially all of the movement caused by the expansion and contraction of the crystalline sections will vbe transmitted to the actuating member 2.

Suitable electrodes 18 and 19 of a thin eo ductor', such as tin foil, are secured to the outside faces of the crystalline sections in any suitable manner, such as by shellac or paraflin, but extend only to a point below the top and above the bottom of said crystalline sections 13 and 14 in order to leave a. suflicient gap between the ends of these electrodes and i the frame which forms the other electrode of the device. A suitable connector, such as a light springclamp 20, connects the electrodes 18 and 19, and is provided with a lead 21 for connection to an outside source of electromotive force. The frame is also provided with a lead 22, which provides the other terminal'for connection to the source of electromotive force. a v

' In order tominimize the effect of the ex pension and contraction of the crystalline sections 13 and 14. of Rochelle salt type upon.

changesofteniperatur'e which is greater than that of the light metal frame, it is preferable to mountthe crystalline sections betweenlthe actuating member 2 and the supporting m mher 8 under compression. One'm'ethodofiaccomplishing this is to apply a force to the actuatm member 2 and the support 8 so as to lacet ethin metal section 7 in tension. The atter, however, is not stretched sufficiently to approach its elastic limit. While it is still in tension, the crystalline sections 13 and 14 are placed in position between the actuating member 2 and the support 8, and if theyare cemented in position the cement is allowed harden before thestension-is released.

The crystalline sections 13 and 14 are preferably selected of such length so that they will not permitthe metal to return to its normal position, thus keeping the thin metal sec- ,tion partially in tension and placing the sections under longitudinal compression.

The result of this arrangement is to practically eliminate the ill efiects of temperature chan s. If thetemperature is raised, the crysta 'ne sections expand more than the thin metal section 7, and the compression of the crystalline sections'is increased and the thin metal section 7 is stretcheda little more. Since the crystalline sections withstand ,compression much better than tension, and since the thin metal section can be stretched still further without exceeding the elastic limit, no harmful effects follow the temperature rise. If, on the other hand, the'temperature falls below the tem rature at which the device was assemble the crystal plates contract faster than'the t in metal section, due to the-fact that they h ve a greaterthermal expansion coeflicient, but the thin metal section has an additional shortening due to the 'release of the tension and thus maintainsthe crystalline sections under some compression between the shoulders.

It will be seen that it is preferable to have the vane 7 relatively thin, so that it will not cause too great a compression on the crystalline sections 13- and 14.

It will also be seen that a similar result can be obtained by assembling-the device at a temperature below any to which the device will be exposed, which will, of course, due to the greater-expansion of the crystalline sections upon temperature rise, place the metal section 7 in tension at normal temperature;

In cases where this stretching was not employed. the crystalline sections were often cracked when the temperature was reduced, owing to the tension developed, as plates made from crystals of saltsof the Rochelle type are comparatively weak in tension. In cases where cracks did not develop, the musical reproduction sometimes became ver poor, due to the loosening of the crystalline sections from the metal arts. r

It should be noted, owever, that the crystalline elements should not be placed in too great compression as this may impair the musical reproduction.

It is referable to cement the ends of the crystalline sections 13 and 14 to the actuating member 2 and the support 8 in order to compensate for any slight differences in length between the crystal portions, and in order to hold them securely in place between the shoulders 9, 10, 11 and 12. It may also be desirable to cement the crystal sections to the faces of the thin metal section 7. I

In constructing this device, any suitable cement for connecting the crystal sections to the metal frame may be used such as Canadabalsam, duco, copper mercury amalgam, or others. The copper mercury amalgam is especially useful in securing a good contact at the ends. as it expands slightly upon hardening.

' If an electrically conductive cement be used it should not overlie the outside faces of the crystalline sections 13 and 14 sufliciently to make contact with the electrodes 18 and 19.

It will also be seen that by making the vane 7 and crystalline sections 13 and 14 progressively smaller in a direction away from the support 9, the stresses caused by the bending moment will be more nearly uniform. Moreover, the mass to be moved will be progressively reduced in those regions where the motion becomes a maximum.

If desired, the whole device may be coated with a protecting varnish or duco after the terminal clip 20 is applied.

hen an electromotive force is applied, the tinfoil electrodes upon the outside of the crystal plates have a potential difference from the inside thin metal strip or inside faces of the plates, and an electrostatic field is set up in the plates in opposite directions, and the plates being oriented as previously described, one plate contracts and the other expands, producing a bending moment which deflects the metal frame and causes a move ment of the actuating member 1 relative to the support 9. Since the support 9 is held fixed by the lead block the motion is transmitted to the conical sound radiating element. hen the applied electromotivc force is reversed, the movement of the sound radiating element is reversed.

The movement of the sound radiating ele ment is much larger than the actual expansion or contraction of the crystalline section as may be readily understood by referring to Fig. 3. Here the full lines show the normal position of the device and the dotted lines show in an exaggerated form the position of the device when an electromotive force has been appli a i to the terminals. The crystalline sectior on one sideis expanded longitudinally and the cyrstalline section on the other side i contracted longitudinally, thus exerting unequal pressure on the shoulders of the actuating member. Since a geometrical element of the central vane remains at constant length and the crystalline.

other side is contracted, a bending moment.

is produced which imparts a,tilting motion to the actuating member of the metal frame, thus moving the conical sound radiating element in a plane substantially at right angles to the plane of the crystalline sections.

While the effect of the sections on the shoulders resulting in the tilting of the'actuating member is probably increased when the sections 13 and 14 are caused to adhere closely to the central vane, it has been found that when the sections are'not secured to the central vane, a. sufficient movement of the actuating member may be obtained to produce satisfactory operation.

It will be noted that the thin vane 7 which connects the base and actuating member 2 affords a reinforcement for the crystalline sections 13 and 14, and the sections are fur-" therprotected bythe shoulders 9 and 12 of the base and the shoulders 10' and 11 of the actuating member 2, so that the sections are less susceptible to breakage fro-m mechanical shocks. The vanei' also affords a convenient structural member to which the sections may be secured, but it is to be understood that any method of securing the sections for longitudinal expansion and contraction, and for causing them to move the actuating member 2 with respect to the base, can be used.

While it is preferable to use a light metal for the frame, it may be noted that other light materialhaving a suitable strength and rigidity to cooperate with crystalline elements may be used.

It will also be seen that since only portions of a crystal need be used in accordance with my invention, economy of piezo-electric material is obtained, as those portions may be cut from imperfect crystals or a fragment of a crystal.

' Since the vane and shoulders provide a mechanical support and reinforcement for the crystal sections, it is unnecessary to embed the ends of the crystal sections in the cement used to attach them to the frame, and consequently the entire length of the section remains effective for a producing motion.

Furthermore, it is to. be understood that the particular forms of apparatus shown and described, and the particular procedure set forth, are presented for purposes of explanation and illustration, and that various modifications of said appartaus and procedure can be made without departing from my invention as defined in the appended claims.

That I claim is:

1. A. piezo-electric device comprising, in combination, a metallic frame including a fixed base and an actuator connected thereto by a longitudinally resilient connecting means, a plurality of expansible members mounted between the base and actuator mider compression, said expansiblemembers being so mounted that upon the application of -including a fixed base and an actuator connected thereto, said base and actuator being rovided with opposing abutments, a plurality of crystalline sections of piezo-electric material mounted between said abutments to normally engage the same, saidsections being so mounted that when subjected to electrostatic fields simultaneous expansion and contraction take place, whereby a movement of the actuator in a direction substantially transverse to the direction'of expansion is produced.

3. A piezo-electric device comprising, in

combination, a metallic frame including a base andan actuator connected thereto by a longitudinally resilient connecting means, a pair of sections of piezo-electric material mountedbetween the base and actuator under compression so that upon the application of an electromotive force to the faces of the sections one of the sections will expand and the other will contract, whereby the actuator is caused to vibrate in a direction transverse to the direction of expansion.

4. A piezo-electric device comprising, in

combination,'a base and an actuator, said baseand actuatorhaving opposing abutments and being connected together with a longitudinally resilient connecting means, a pair of sections of piezo-electric material mounted between said base and actuator under compression, and in positionto cause movement of the abutments of the actuator in a direction substantially transverse to the direction of expansion and contraction of the piezoelectric sections, means for applyingan electromotive force to the faces of the piezoelectric sections to cause the expansion of one and the-contraction of the other simultaneously, and an acoustic element connected to said actuator.

5. A piezo-electric device comprising, in combination, a base and an actuator, said base and actuator being connected together by a relatively thin, longitudinally resilient connecting means of relatively. light metal, a pair of sections of piezo-electric material secured to said connectingmeans and having their opposite ends normally engaging said base and actuator, electrodes attached to the outer surface of said sections so that upon the application of an electromotive force to the faces of the sections one section will expand and the other will contract to cause movement of the actuator with respect to the base in a direction substantially transverse to the direction of expansion and contraction of the sections, and a sound radiating element secured to said actuator.

6. A piezo-electric device comprising, in

combination, a fixed base and an actuator,

said base and actuator being connected together by a relatively thin, longitudinally resilient connecting means, a pair of sections of piezo-electric material disposed adjacent said connecting means and adapted to engage the base and acuator,said sections being secured to the base and actuator and b ing under compression, so that upon the appli'cation of an electromotive force to the faces of the sections one section expands and the other contracts to cause movement of the actuator with respect to the base in a direction substantially transverse to the direction of exansion.

7. The method of producing a piezo-electric device having a metallic frame, comprising an actuator connected by a longitudinally resilient means to a fixed base, tensioning the longitudinally resilient connecting means, positioning sections of piezo-electric material between the base and actuator, and adjacent the connecting means, cementing the sections in position, and releasing the tension Y on the connecting means after the cement has hardened.

8. The method of producing a piezo-electric'device having a metallic frame, comprising an actuator connected by a longitudinally resilient means to a fixed base, tensioning the longitudinally resilient connecting means, positioning sections of-piezo-electric material between the base and actuator in opposed-relation, so that upon the applica-' tion of an electromotive force one section will expand and the other will contract, and

. actuator for causing movement of the actuator upon the application of electromotive force to the-piezo-electric material, said actuf ator and connecting means being constructed of metal having a relatively low specific avity and having a relatively high coefliient of thermal ex ansion.

10. A piezo-electric acoustic device come; rising a frame including a base, an actuator or an acoustic diaphragm and a longitudinally resilient connecting means connecting the actuator and base, sections of piezo-electric material of the Rochelle salt type disposed under compression between the base and actuator for causing movement of .the actuator upon the apphcation of electiomo-j tive force to the piezo-electric material, said connecting means being constructed of metal having a relatively low specific gravity and having a relatively high coefficient of thermal expansion.

11. In a loud speaker, in combination, a metallic frame including a base and a support, a sound reproducing surface carried by said support, said support and base being con nected together by a relatively thin longitudinal member and being provided with opposing abutments, a plurality of crystalline sections of piezo-electric material mounted between said abutinents, said sections being mounted so that when subjected to electrostatic field simultaneous expansion and contraction takes place, whereby a bending movement is produced and said support transmits motion directly to said sound reproducing surface.

12. In a loud speaker, the combinationwith a sound reproducing surface, ofa base and a support connected together, said sound reproducing surface being carried by said support, sections of piezo-electric material disposed under compression between the base and support for causing vibration of the support upon the application of an electromotive force to the piezo-electric material, said piezo-electric sections being arranged to simultaneously expand and contract to cause a a transverse vibration of the support upon the application of electromotive force, and a consequent vibration of the sound reproducing surface.

13. A piezo-electric device comprising, in combination, a frame, including a fixed base and an actuator connected thereto by a resilient connecting means, said base and actuator being provided with opposing abutments, a plurality of crystalline sections of pieZo-electric material mounted between said abutments under compression, said sections bein so oriented that they are disposed in oppose electrostatic relation, and so positioned between theiabutments that a longitudinal expansion of one section is accompanied by a longitudmal contraction of an opposed section, said sections of piezo-electric material having electrodes secured to the outside surfaces of the crystalline sections.

In testimony whereof I afiix m signature.

CHARLES B. S WYER. 

